Integrated circuits are formed on and in semiconductor substrates using a number of different processing operations that create circuit elements. In order to access circuitry associated with the semiconductor substrate, bond pads are formed on the integrated circuits. Bond pads provide the means for transfer of electrical signals and power from and to the circuit elements via probes, bonding wires, conductive bumps, etc.
The bonding pads and the conductive elements thereto must be electrically conductive to form part of the desired electrical connections and, therefore, they are typically made from a metal or metal alloy. Until recently, aluminum (Al) has been the metal of choice for making bonding structures for integrated circuits. However, industry preferences for smaller and more densely packed active circuit components has led to the wider use of copper (Cu) and copper alloys as a substitute for aluminum. Copper has a higher electrical resistivity than Al and, because copper is electropositive, it is less vulnerable to electro-chemical corrosion. However, adhesion and reliability of the bonds between bonding structures and conductive elements are primary concerns to ensure proper and continued functioning of the integrated circuits and active circuit components thereon. Copper is more susceptible to chemical corrosion in air and, therefore, copper oxides tend to form when in contact with air and moisture. As a result, when aluminum or gold wires are electrically connected to copper bonding structures, the bond between the wire and the bonding structure is susceptible to corrosion, oxidation and thermal diffusion problems.
To protect the surface of a copper bonding structure and thereby facilitate formation of a reliable bond between the conductive element and the copper bonding structure, some bonding structures have been formed with a protective cap layer made of another metal, e.g., aluminum, aluminum alloy, tungsten, titanium, or a phosphorus- or boron-containing metal alloy, that is deposited over the surface of the copper bonding structure. More recently, to reduce costs and improve passivation, silicon nitride (SiN) deposited by plasma enhanced vapor deposition (PECVD) has been suggested to replace the metal-containing materials to form passivation layers over copper-containing bond pads. This has resulted in bonding structures having passivation layers with some satisfactory properties. However, the deposition rate via PECVD has been found to be too quick and has not provide sufficient control to produce a SiN layer of the desired minimal thickness and high uniformity. Additionally, greater levels of passivation are required than can be achieved by SiN passivation layers on copper bonding structures.
Accordingly, it is desirable to provide integrated circuits having copper bonding structures with passivation layers thereon that provide improved protection from corrosion. It is further desirable to provide methods for fabricating such integrated circuits. Other desirable features and characteristics of the integrated circuits and method disclosed herein will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background discussion.